1. Field of the Invention
The present invention relates to an artificial intervertebral disk to replace a damaged human disk between two adjacent vertebrae in a human spinal column. More particularly, the invention relates to an artificial intervertebral disk which is secured in place between two adjacent vertebrae and maintains the full range of rotational motion that the natural disk provided.
2. Description of the Background Art
Throughout the United States steps are being taken artificial intervertebral disks. A common curse of humankind is a ruptured or herniated disk. The function of the human disk is to maintain separation between the adjacent vertebrae comprising the spinal column. A human spinal column has 5 vertebrae in the lumbar region and seven vertebrae in the cervical region and 12 vertebrae in the thoracic region. The lumbar region is commonly referred to as the lower back and the cervical region is commonly referred to as the neck. The thoracic region is in the middle of the spinal column. The spinal column is the primary structural element of the human skeleton. It is required to carry the compressive load of the upper portion of the body and transmit that load to the lower portion of the body. Consequently, it must have the compressive structural strength needed to perform that role over millions of cycles. Also, the spinal column must support the body under the normal human activities such as bending, turning, stooping over and engaging in various forms of exercise. To accommodate this requirement, the spinal column must be capable of rotational twisting without breaking. The dual role is accommodated by the inter-positioning of a human disk between the adjacent vertebrae in the lumbar region and the cervical region and the thoracic region. The function of the human disk is to provide the compressive strength necessary to avoid having the adjacent vertebrae come in contact with each other. For example, the conventional surgical approach for a ruptured cervical disk is to remove the damaged cervical disk and fuse the space now developed between the adjacent vertebrae with a bone graft. Repair plates for anterior cervical fusion are known in the art. For example, a "caspar" repair plate is produced by the Aesculap Corporation of Burlingame Calif. It is disclosed under U.S. Pat. No. 4,503,848. Anterior cervical fusion has the disadvantage of reducing the range of rotational motion, due to the joining of the adjacent vertebrae. Over time, the range of motion reduction can be significant if more than one fusion is performed, particularly in the cervical region. Furthermore, it causes degeneration of the disk spaces above and below the levels of fusion.
Many artificial disk have been developed to replace a damaged human disk. However, none are completely satisfactory.
U.S. Pat. No. 4,874,389 issued to Downey discloses a replacement disk having two interengaged loops surrounded by an elastomeric body.
U.S. Pat. No. 4,946,378 issued to Hirayama et al. discloses an artificial intervertebral disk having a pair of end bodies and an intermediate elastic material.
U.S. Pat. No. 4,759,769 issued to Hedman et al. discloses an artificial disk having a hinged upper piece and a hinged lower piece with a coil spring therebetween.
U.S. Pat. No. 4,997,432 issued to Keller discloses an intervertebral disk having stop plates with two projections and a sliding core held between the stop plates.
U.S. Pat. No. 3,987,499 issued to Scharbach et al. discloses an implant for a hip bone having an upper and lower piece with a pin securing the upper and lower pieces.
U.S. Pat. No. 4,759,766 issued to Buettner-Janz et al. discloses an intervertebral disk having an upper and lower plate with an intermediate plate therebetween.
U.S. Pat. No. 4,932,975 issued to Main et al. discloses a prosthesis having a vertical body with a suspension medium surrounding a suspension plate.
U.S. Pat. No. 5,123,926 issued to Pisharodi discloses an artificial disk having a plurality of spring loaded cups positioned within a prosthesis for urging the implant to conform to the space between the adjacent vertebrae.
U.S. Pat. No. 5,071,437 issued to Steffee discloses a spinal disk prosthesis having an upper and lower plate with an elastomeric core sandwiched between the upper and lower plate.
U.S. Pat. No. 4,636,217 issued to Ogilvie et al. discloses a prosthetic implant held in place by screws in the adjacent vertebrae.
None of these previous efforts, however, provide the benefits intended with the present invention. Additionally, prior techniques do not suggest, the present inventive combination of component elements as disclosed and claimed herein. The present invention achieves its intended purposes, objectives and advantages over the prior art devices through a new, useful and unobvious combination of component elements, which is simple to use, with the utilization of a minimum number of functioning parts, at a reasonable cost to manufacture, assemble, test and by employing only readily available material.
Therefore, it is an object of the present invention to provide a artificial intervertebral disk which can be used in place of the damaged human disk and maintain the full range of motion heretofore enjoyed by the person.
It is a further object of the invention to provide an artificial intervertebral disk to maintain the full separation distance between the adjacent vertebrae heretofore enjoyed by the person.
It is a still further object of the invention to provide an artificial intervertebral disk that is biochemically stable and biocompatable with the human skeletal system and tissue.
It is another object of the invention to provide an artificial intervertebral disk that will encourage rapid adherence to the surrounding bone and tissue after the implantation.
It is still another object of the invention to provide an artificial intervertebral disk that can be implanted in the person with standard surgical drills and drill bits.
It is another object of the invention to provide an alignment and holding tool to enable the surgeon to implant the artificial intervertebral disk with consistent alignment of all the components of the invention.
It is another object of the invention to provide an artificial intervertebral disk that is maintained in the same relative position in the spinal column by means of fasteners securely engaged to the bone material and to the threaded recesses in the cylindrically shaped members.
It is a final object of the invention is to provide an artificial intervertebral disk that can be implanted in a patient with their respective ball and socket members oriented in a upper and lower relationship that has equally satisfactory outcomes either when the ball member is oriented above the socket member or when the respective positions are reversed.
Although there have been many inventions related to an artificial disk, none of the inventions have become sufficiently compact, low cost and reliable enough to become commonly used. The present invention meets the requirements of a simplified design, compact size, low initial cost, ease of implantation and maintainability, and minimal amount of training to successfully employ the invention. The artificial disk of the present invention is easy to manufacture, maintenance free, and biochemically stable when implanted in the human spinal column.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.